Optical network technology is moving towards providing fibre to the home utilizing wavelength division multiplexing (WDM). One particular solution for fibre to the home is wavelength division multiplexed passive optical networks (WDM-PON) in which a separate wavelength channel is used to communicate from the central office (CO) optical line termination (OLT) to the optical network unit (ONU) at each home. This approach creates a virtual point-to-point link between the CO and each ONU, in contrast to the point to multipoint topology of a regular PON. The WDM-PON network architecture requires that each ONU transmits upstream on a different wavelength. Providing each ONU with a different fixed wavelength transmitter is a costly approach and has maintenance problems associated with it. An alternative, more attractive, approach is to provide tunable lasers as the transmitters in each ONU. However, using tunable lasers at the ONUs faces the problem of tuning each laser to the correct wavelength for its associated channel.